The paper discusses Tycho Brahe’s geo-heliocentric system, arguing that it represents a good instance of a failed synthesis. First, the Author analyzes the physical and metaphysical principles grounding this system, relying on Brahe’s correspondence with Christoph Rothmann. The popular anti-Copernican arguments of the tower and of the cannon, which Galileo would try to refute in his Dialogue Concerning the Two Chief World Systems, find here their first formulation. Secondly, some theoretical problems of Tycho’s system are discussed, intending also to clarify Galileo’s ambiguous attitude towards him. Indeed, although Brahe is surely the major polemical reference of Galileo’s Dialogue, he is never explicitly mentioned therein. This is because, as Galileo says, Tycho was never able to provide a thorough description of a system of the world comparable to those of Ptolemy and of Copernicus. Brahe’s system may thus be characterized as the last great attempt to synthetize the old and the new, before the risk of the collapse of the traditional cosmos: attempt which, considering the growing success of the heliocentric model, was inevitably doomed to failure.
Keywords: Tycho Brahe, geo-heliocentric system, Galileo Galilei, Ptolemy, Nicolaus Copernicus